Research On Coordinated Control Strategy Of Multiple Reactive Power Devices In The Near Region Of UHV DC Drop Point

In the context of China’s extremely uneven energy distribution,UHV DC transmission has many unique advantages such as large transmission capacity,small line loss,and long transmission distance.In recent years,many UHV DC lines have been put into production in succession.The load continues to increase,the DC transmission power continues to increase,and the proportion of new energy is increasing year by year.The coupling relationship between AC and DC systems is closer.Due to the large-scale use of power electronics in DC transmission systems,a large amount of reactive power is consumed during steady state operation.Increased pressure on reactive support demand,leading to failure of the AC system at the receiving end may lead to DC commutation failure or even DC blocking.Improving the dynamic reactive power support capability of the receiving end is an urgent problem to be solved.This article conducts research on the coo rdination and optimization of multiple reactive power devices near the UHV DC drop point.The existing reactive power sources in the system are used to improve the voltage stability of the power grid,mainly including the following:First,the mechanism simulation analysis of the reactive voltage characteristics of common components in the receiving end power grid is performed,and the negative impact of parallel capacitors and a large number of power electronic devices in the DC system on voltage stability is pointed out.According to the research on the reactive voltage characteristics of the generator,it is found that the more the generator’s steady-state reactive power output,the more dynamic reactive power can be provided after a fault.Based on this research,the steady-state operation time was verified through small system simulation.Increasing the reactive power output of the generator will also improve the voltage stability of the power grid.Then,the comprehensive evaluation index of the generat or is proposed,which includes the evaluation index of the effective reactive power reserve of the generator considering the steady-state reactive power output of the generator and the evaluation index of the dynamic reactive power support of the generator.The evaluation index of effective reactive power reserve fully considers the generator’s transient reactive power support margin,and can more accurately reflect the generator’s transient effective reactive power reserve capacity.The generator dynamic reactive power support evaluation index takes into account the trajectory of generator dynamic reactive power output change with time,converter bus voltage recovery speed,and voltage boost contribution.Finally,a coordinated optimization control method for multi-reactive devices with different voltage levels is proposed,and a multi-reactive device ratio strategy at different spin-up levels is presented.Taking the Central China Power Grid’s 2019 grid as an example,the proposed method is applied to the actual system,and it is verified that the method can effectively improve the stability of the receiving grid voltage and has good economics.Combined with the planning and construction of the Central China Power Grid UHV ring network in the next 2-3 years,the huge impact of the grid structure on the stability of the power grid has been verified.The voltage regulation method of increasing the generator terminal voltage can increase the stability margin of the receiving end grid.The universal applicability of this method.